1. Field of the Invention
The present invention relates generally to radiation sensors and more particularly relates to a relatively low frequency probe capable of both E-field and H-field measurement.
2. Description of the Prior Art
Field measurements from electromagnetic sources are commonly performed to determine the intensity of an electric field (E-field) and a magnetic field (H-field) at a given location. The intensities of these fields are determined in order to ascertain the radiation hazards to human beings in an area and also to conduct controlled radiation tolerance tests on various equipment. In performing these measurements, it is preferred that accurate, frequency independent measurements can be taken of both the E and H fields at fairly low frequencies (i.e., from about 0.1 to about 300 megahertz).
U.S. Pat. No. 4,588,993 to Babij, et al. is directed to an isotropic probe system for simultaneous measurement of E and H fields. The device disclosed employs a combination of three perpendicular dipole antennas to measure E-field radiation in combination with three perpendicular loop antennas to measure H-field radiation. However, the electrically small dipoles disclosed in the Babij patent present a substantial impedance at low frequencies. This high impedance significantly diminishes the sensitivity performance at low frequencies.
U.S. Pat. No. 5,057,848 to Rankin, et al. is directed to a broadband frequency probe. The '848 patent teaches the use of a three-dimensional probe having three mutually orthogonal antenna pairs. Each antenna pair includes a high frequency monopole antenna and a low frequency disc antenna. However, neither of the two elements in each pair is responsive specifically to H-field radiation. Therefore, a device formed in accordance with the '848 patent cannot simultaneously measure both the E-field and H-field intensity from an electromagnetic source. Rather, each of the antenna elements is selected to be responsive only to E-field radiation in a portion of the frequency band of operation.